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| 3. |
- Ebbestad, Jan Ove R., et al.
(författare)
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Ordovician of the Siljan District, Sweden
- 2007
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Ingår i: Sveriges Geologiska Undersökning, Rapporter och Meddelanden. - 0349-2176. ; :128, s. 7-26
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Jeppsson, Lennart, et al.
(författare)
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Biostratigraphy of Gotland
- 2005
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Ingår i: The Dynamic Silurian Earth (Rapporter och Meddelanden). - 0349-2176. - 9171587144 ; 121, s. 14-17
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Jeppsson, Lennart, et al.
(författare)
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Field localities
- 2005
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Ingår i: The Dynamic Silurian Earth (Rapporter och Meddelanden). - 0349-2176. - 9171587144 ; 121, s. 22-56
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Lynch, Edward, et al.
(författare)
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Geology, lithostratigraphy and petrogenesis of c. 2.14 Ga greenstones in the Nunasvaara and Masugnsbyn areas, northernmost Sweden
- 2018
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Ingår i: SGU Rapporter och meddelanden. - Uppsala : Sveriges geologiska undersökning. - 0349-2176. ; 141, s. 19-77
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Tidskriftsartikel (refereegranskat)abstract
- Two Palaeoproterozoic greenstone successions in the Nunasvaara and Masugnsbyn areas of north-central Norrbotten (northernmost Sweden) have been investigated to (1) characterise their primary depositional features; (2) establish lithostratigraphic correlations between both areas; and (3) gain insights into the petrogenesis of greenstone-type volcano-sedimentary successions in this sector of the Fennoscandian Shield.In the Nunasvaara area (Vittangi greenstone group), a partly conformable, polydeformed, approximately 2.4 km thick greenstone sequence mainly consists of basaltic (tholeiitic) metavolcanic and metavolcaniclastic rocks (amygdaloidal lava, laminated tuff). Intercalated metasedimentary units include graphite-bearing black schist, and pelite. The uppermost part consists of amphibolitic pelite with intercalated metacarbonate layers and rare meta-ironstone, metachert and meta-ultrabasic horizons. Numerous metadoleritic sills occur throughout the package.In the Masugnsbyn area (Veikkavaara greenstone group) a relatively conformable approximately 3.4 km thick greenstone sequence displays lithological, geochemical and geophysical characteristics similar to that at Nunasvaara. This succession consists of a dominant basaltic metatuff sequence overlain by metasedimentary units towards the top (e.g. meta-ironstone, metachert, amphibolitic schist, calcitic and dolomitic marbles). Minor metadolerite sills occur in the metatuffs. Near the base of the metatuff package, a graphitic black schist horizon occupies a similar stratigraphic position to a prominent black schist layer at Nunasvaara (here named the Nunasvaara member). This unit is a key marker horizon providing lateral correlation between both successions and also acts as a useful strain marker for reconstructing deformational events.Both greenstone successions record the effects of overprinting syn-to late-orogenic (Svecokarelian) tectonothermal events. These include complex, polyphase ductile deformation (D1 to D3 events at Nunasvaara, forming the Nunasvaara dome), peak amphibolite facies metamorphism, metasomatic-hydrothermal alteration and late-stage retrogression and brittle faulting (composite D4 at Nunasvaara). Locally, these overprinting processes formed metamorphic graphite, skarn-related Fe ± Cu and hydrothermal Cu ± Pb ± Mo mineralisation.U-Pb SIMS zircon dating of a metadolerite dyke from Nunasvaara and a metadolerite sill from Masugnsbyn have yielded mean weighted 207Pb/206Pb ages of 2 144 ±5 Ma (2σ, n = 10) and 2 139 ±4 Ma (2σ, n = 5) Ma, respectively. These precise dates constrain the timing of hypabyssal mafic magmatism, provide a minimum age for the deposition of the volcanic and sedimentary rocks, and identify a new approximetly 2.14 Ga episode of tholeiitic magmatism in this sector of the Fennoscandian Shield. Whole-rock initial εNd values for greenstone meta-igneous units range from +0.4 to +4.0 at Nunasvaara (n = 11) and +0.4 to +3.7 at Masugnsbyn (n = 7). These data indicate a juvenile depleted to partly enriched mantle (asthenospheric or lithospheric) as a major source of the tholeiitic melts. Corresponding trace element systematics have enriched mid-ocean ridge (E-MORB)-type signatures, and indicate minor assimilation of Archaean continental crust (i.e. Norrbotten craton) during magma ascent and storage. Overall, the combined geological, geochemical and isotopic characteristics of the greenstones are consistent with protolith formation within an incipient oceanic basin (epieric Norrbotten Seaway) during approximetly 2.14 Ga rifting and sagging of the Norrbotten craton.
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| 7. |
- Lynch, Edward, et al.
(författare)
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Petrological and structural character of c. 1.88 Ga meta-volcanosedimentary rocks hosting iron oxide-copper-gold and related mineralisation in the Nautanen–Aitik area, northern Sweden
- 2018
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Ingår i: SGU Rapporter och meddelanden. - Uppsala : Sveriges geologiska undersökning. - 0349-2176. ; 141, s. 107-150
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Tidskriftsartikel (refereegranskat)abstract
- The petrological and deformation characteristics of a Palaeoproterozoic meta-volcanosedimentary sequence in the Nautanen–Aitik area (near Gällivare, northern Sweden) are presented. The investigated sequence (part of the Muorjevaara group) predominantly comprises metavolcaniclastic rocks displaying variable grain size, textural and syn-depositional features (e.g. grading, cross-laminae, compositional banding). Locally, poorly sorted agglomerate-like horizons with coarser clasts (lapilli-to block-size) occur. Interbedded sections of mainly fine-grained, volcanogenic (epiclastic) metasedimentary rocks contain syn-depositional features that suggest a sub-aqueous, relatively shallow depositional environment. Locally preserved cross-laminae in this unit provide evidence of way-up and paleocurrent directions. Intercalations of pelite, mica schist and amphibolitic schist also occur throughout the sequence. In general, least altered samples indicate a predominantly intermediate (basaltic andesitic to andesitic), calc-alkaline composition for the sequence.U-Pb SIMS zircon dating of a meta-andesite horizon, intercalated within the sequence, has yielded a precise U-Pb concordia age of 1 878 ± 7 Ma (2σ, n = 12). This date constrains the timing of intermediate volcanism and the deposition of syn-volcanic epiclastic material. By inference, it also provides an estimate for the age of Muorjevaara group rocks hosting the Nautanen Cu-Au and Aitik Cu-Au-Ag deposits. When combined with lithogeochemical signatures, the new age also confirms a genetic link between the metavolcaniclastic package and gabbroic to dioritic intrusions in the area (e.g. the c. 1.88 Ga Aitik stock). Additionally, several zircon cores record 207Pb/206Pb apparent ages between c. 1.90 and 1.89 Ga, suggesting inheritance of marginally older volcanic ± plutonic material not exposed at the present erosion level.The Nautanen–Aitik area contains the roughly north-northwest-trending Nautanen deformation zone (NDZ), a major composite brittle-ductile structure hosting hydrothermal iron oxide-Cu-Au (IOCG)-style mineralisation (e.g. the Nautanen deposit). Here, the bedrock is relatively intensely altered and sheared, and has been transposed into a sub-parallel high-strain zone predominantly consisting of a composite planar penetrative fabric. Outside the high-strain zone, relatively large-scale approximately north-northwest-aligned folds and discordant brittle structures occur. Magnetic susceptibility and VLF-resistivity modelling of the NDZ confirm that composite planar structures mainly dip steeply to the west-southwest and continue at depth.
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| 8. |
- Martinsson, Olof, et al.
(författare)
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Age and character of late-Svecokarelian monzonitic intrusions in northeastern Norrbotten, northern Sweden
- 2018
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Ingår i: SGU Rapporter och meddelanden. - Uppsala : Sveriges geologiska undersökning. - 0349-2176. ; 141, s. 381-400
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Tidskriftsartikel (refereegranskat)abstract
- Palaeoproterozoic magmatism in northern Norrbotten shows a complex evolution, with several different plutonic suites ranging in age 1.93–1.70 Ga. Here we present data for three monzonitic intrusions from different parts of the area. They are petrographically and chemically similar, consisting mainly of perthite, augite and orthopyroxene, with megacrysts of poikilitic biotite as a characteristic minor component, and with high Sr and Ba. The intrusions have been dated at 1.80 Ga and may be part of a more extensive magmatic event in northern Sweden, including other chemically similar monzonitic and gabbroic intrusions, which often occur as ring dykes at the Merasjärvi gravity high (MGH) in northeastern Norrbotten. The monzonitic intrusions have A-type signatures and chemical characteristics overlapping those of rocks in arc and within-plate settings. These intrusions may thus have formed in either a back arc setting related to eastward subduction associated with the Transscandinavian Igneous Belt further west (TIB 1), or through a separate igneous event caused by a mantle plume.
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